Traditionally with a conventional hypodermic syringe a practitioner, or user, must stop depressing a plunger based on visual feedback, typically from a scale on the hypodermic syringe. Consequently, it is difficult to perform a repeated dose injection with a high degree of accuracy and/or precision.
In U.S. Pat. No. 5,318,544 is disclosed a syringe for metering precise volumes of fluid without having to use a visual volumetric scale. The document discloses a syringe container adapted for receiving a plunger containing a plurality of stop surfaces which are angularly and linearly displaced about a longitudinal axis of said plunger. Translation of the plunger brings a first stop surface into contact with a stop edge of the syringe container. The plunger is then rotated to release the first stop surface from the stop edge, thereby permitting the plunger to be translated until a second stop surface contacts the stop edge. During translation of the plunger, a predetermined volume of fluid is metered through an orifice. This allows a user to administer predetermined volumes of fluid, precisely metered through the orifice, without having to read a scale of volumetric units and without requiring the user having to control the stopping action of the plunger.
The disclosed prior art lacks of indicator means. The lack of indicator means confuses a user to know whether or not the medicament delivery device is ready to use.
There is therefore a need for an arrangement that can provide both expelling repeated doses in a precise, easy and controlled manner having means for easily indicating the enablement or disablement of the device when a user aims to eject a predetermined volume of medicament. Thus, as can be noted, human handling aspects of a medicament delivery device are crucial and there are several rationales for improving existing solutions.